Method for simulating power supply noise in an on-chip temperature sensor

ABSTRACT

A method for estimating accuracy of an on-chip temperature sensor is provided. A representative power supply waveform having noise is input into a simulation of the on-chip temperature sensor and the accuracy of the on-chip temperature sensor is estimated from the simulation. A computer system for estimating accuracy of an on-chip temperature sensor is also provided. A computer-readable medium having instructions adapted to input a representative power supply waveform having noise into a simulation of an on-chip temperature sensor and estimate accuracy of the on-chip temperature sensor from the simulation is provided.

BACKGROUND OF INVENTION

[0001] To increase processor performance, clock frequencies used bymicroprocessors, often referred to as “CPUs,” have increased. Also, asthe number of circuits that can be used in a CPU has increased, thenumber of parallel operations has risen. Examples of efforts to createmore parallel operations include increased pipeline depth and anincrease in the number of functional units in super-scalar andvery-long-instruction-word architectures. As processor performancecontinues to increase, the result has been a larger number of circuitsswitching at faster rates. Thus, from a design perspective, importantconsiderations such as power, switching noise, and signal integrity mustbe taken into account.

[0002] Higher frequencies and data throughput cause a processor toconsume increased power and run at increased temperatures. Extremetemperatures can slow the speed of transistors that may cause some CPUactivities to be incomplete at the end of a cycle. The effect may leadto loss of data in a CPU or incorrect results; therefore, on-chiptemperature sensors are employed for monitoring. The availability oftemperature information allows the CPU to reduce the number ofactivities and/or slow the operating frequency. If scaling the number ofactivities does not alleviate the condition, a standby or power downmode may be entered to protect the CPU. Accurate temperature informationis important to prevent over heating or unnecessary reduction in CPUactivities.

[0003] Higher frequencies for an increased number of circuits alsoincreases switching noise on the power supply. The switching noise mayhave a local or global effect. Circuits that create large amounts ofnoise may be relatively isolated; however, they may also affect othercircuits, possibly involving very complex interactions between the noisegeneration and the function of affected circuits. If the componentsresponsible for carrying out specific operations do not receive adequatepower in a timely manner, computer system performance is susceptible todegradation. For example, on-chip temperature sensor accuracy varieswith power supply noise. Thus, providing power to the components in acomputer system in a sufficient and timely manner has become an issue ofsignificant importance.

[0004]FIG. 1 shows a section of a typical power supply network (10) of acomputer system. The power supply network (10) may be representative ofa single integrated circuit, or “chip”, or equally an entire computersystem comprising multiple integrated circuits. The power supply network(10) has a power supply (12) that provides power through a power supplyline (14) and a ground line (16) to an impedance network Z₁ (18). Theimpedance network (18) is a collection of passive elements that resultfrom inherent resistance, capacitance, and/or inductance of physicalconnections. A power supply line (22, 23) and a ground line (24, 25)facilitate power supply to a circuit A (20) and circuit B (26),respectively. Power supply line (23) and ground line (25) also supplycircuit C (30) through another impedance network Z₂ (28) and additionalimpedance networks and circuits, such as impedance network Z_(n) (22)and circuit N (34). The impedance network and connected circuits may bemodeled so that the designer, using a simulator, can better understandthe behavior of how the circuits interact and interdependencies thatexist.

[0005] Still referring to FIG. 1, circuit A (20), circuit B (26),circuit C (30), and circuit N (34) may be analog or digital circuits.Also, circuit A (20), circuit B (26), circuit C (30), and circuit N (34)may generate and/or be susceptible to power supply noise. For example,circuit C (30) may generate a large amount of power supply noise thataffects the operation of both circuit B (26) and circuit N (34). Thedesigner, in optimizing the performance of circuit B (26) and circuit N(34), requires an understanding of the characteristics of the powersupply noise.

SUMMARY OF INVENTION

[0006] According to one aspect of the present invention, a method forestimating accuracy of an on-chip temperature sensor comprises inputtinga representative power supply waveform having noise into a simulation ofthe on-chip temperature sensor and estimating accuracy of the on-chiptemperature sensor from the simulation.

[0007] According to another aspect of the present invention, a computersystem for estimating accuracy of an on-chip temperature sensorcomprises a processor; a memory; and software instructions stored in thememory adapted to cause the computer system to input a representativepower supply waveform having noise into a simulation of the on-chiptemperature sensor and estimate accuracy of the on-chip temperaturesensor from the simulation.

[0008] According to another aspect of the present invention, acomputer-readable medium having recorded thereon instructions executableby a processor, the instructions adapted to input a representative powersupply waveform having noise into a simulation of an on-chip temperaturesensor and estimate accuracy of the on-chip temperature sensor from thesimulation.

[0009] Other aspects and advantages of the invention will be apparentfrom the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0010]FIG. 1 shows a typical computer system power supply network.

[0011]FIG. 2 shows a temperature sensor circuit test arrangement.

[0012]FIG. 3a shows a flow process in accordance with an embodiment ofthe present invention.

[0013]FIG. 3b shows a flow process in accordance with another embodimentof the present invention.

[0014]FIG. 4 shows captured power supply waveforms in accordance withanother embodiment of the present invention.

[0015]FIG. 5 shows a circuit in accordance with another embodiment ofthe present invention.

DETAILED DESCRIPTION

[0016] Embodiments of the present invention relate to a method forestimating accuracy of an on-chip temperature sensor. Embodiments of thepresent invention further relate to a computer system for estimatingaccuracy of an on-chip temperature sensor. Embodiments of the presentinvention also relate to a program executed on a computer for estimatingaccuracy of an on-chip temperature sensor.

[0017] In FIG. 1, the impedance networks (18, 28, 32) may be verycomplex arrangements of passive elements. The impedances may be theresult of, but not limited to, a power supply connection, bulkcapacitors, printed circuit board planes, printed circuit board vias,ceramic capacitors, printed circuit board to chip package connections,chip package planes, chip package vias, chip package capacitors, chippackage to chip bump or bond wire connections, chip local and globaldecoupling capacitors, and switching and non-switching circuit elements.A “chip package” for the purpose of this description of the inventionmay be any package that allows mounting an integrated circuit to aprinted circuit board. An integrated circuit, or die, is also referredto as a “chip” in this description. Also, each of the circuits (20, 26,30, 34) in FIG. 1 may induce power supply noise on the impedancenetworks (18, 28, 32). The power supply noise characteristics can resultfrom interactions between the circuits (20, 26, 30, 34) coupled with theimpedance networks (18, 28, 32).

[0018] For a designer to adequately examine the behavior of the powersupply noise, a simulation model is desirable. The simulation model isinput into a simulation tool so that a computer can calculate theeffects of one or more input excitations. One example of a simulationtool is SPICE. Modeling a complex array of impedances is difficult,however. Furthermore, even if an accurate simulation model is created,the computing overhead necessary to simulate one or more circuits withthe impedance model network may be too great.

[0019] In the absence of an accurate model, worst case simulations areoften used. In FIG. 2, a test arrangement (40) for an on-chiptemperature sensor (45) is shown. The on-chip temperature sensor (45) issupplied by a DC power supply (43). In this example, the on-chiptemperature sensor (45) uses a temperature representative input togenerate a temperature dependent output (60) such as a binaryrepresentation of the measured temperature. Ideally, the valuerepresented by the binary representation would linearly corresponds tothe temperature representative input; however, due to power supplynoise, the binary representation may be inaccurate. A low frequencysquare wave used to simulate power supply noise is one of the mostextreme power supply noise tests that can be performed. For example, tomodel the power supply noise, a square wave generator (44) supplies apeak-to-peak voltage signal which is approximately 20% of the DC powersupply (43) voltage. For example, a 0.2 V peak-to-peak square wave maybe used with a 1.0 V DC power supply. The square wave generator (44)signal is added to the DC power supply (43) at adder (46). The combinedDC power supply (43) and square wave generator (44) output is suppliedon power supply line (48) to the on-chip temperature sensor (45). Thevoltage of the DC power supply (43), frequency and amplitude of thesquare wave generator (44), and temperature representative input may bechanged to model different operating points.

[0020] Those skilled in the art will appreciate that the temperaturerepresentative input of an on-chip temperature sensor may be a varietyof different signals including, but not limited to, a temperature, anumerical value representing a temperature, a temperature representativevoltage, and a temperature representative current. Those skilled in theart will also appreciate that the temperature dependent output of anon-chip temperature sensor may have a variety of different signaloutputs including, but not limited to, a numerical value representing atemperature, a binary representation of a temperature, a temperaturedependent frequency, a temperature dependent voltage, a temperaturedependent current, and a temperature dependent pulse width modulation.

[0021]FIG. 3a shows an exemplary flow process (100) in accordance withan embodiment of the present invention. At (102), a power supplywaveform having noise is captured. A power supply waveform having noisefor the purpose of this description may be any power supply that hasdeviations from a designed voltage. This power supply waveform iscaptured at some particular location within a power supply network.Those skilled in the art will appreciate that the noise in the capturedpower supply waveform comes from a dominant source of noise. A circuitunder design does not provide a substantial contribution to the noise inthe captured power supply waveform. The power supply waveform havingnoise may be used to adequately represent a large portion of the powersupply network and associated circuitry.

[0022] In FIG. 1, for example, circuit C (30) may be the dominant sourceof noise. The temperature sensor under design may be circuit N (34). Bycapturing a power supply waveform having noise between impedancenetworks Z₂ (28) and Z_(n) (32), a system response that represents alarge portion of the power supply network and associated circuitry isused. For example, the power supply network and associated circuitry mayinclude the power supply (12), impedance network Z₁ (18), circuit A(20), circuit B (26), circuit C (30), and impedance network Z₂ (28).Because the dominant source (circuit C (30)) is included in the powersupply network and associated circuitry, a simulation using the powersupply waveform having noise, impedance network Z_(n) (32) and circuit N(34) is sufficient.

[0023] With regard to simulating a CPU circuit, capturing a power supplywaveform on a printed circuit board near the CPU is desirable. Thecaptured power supply waveform will also contain noise as a result ofactivities on the printed circuit board by one or more circuits. Thecaptured power supply waveform may be the result of physically measuringthe voltage on the printed circuit board under operating conditions withmeasuring equipment. These operating conditions may include extremeconditions in an effort to capture a worst case power supply waveformhaving noise. These operating conditions may be the result of varyingone or more of the following: temperature, voltage, frequency, andmanufacturing process. The captured power supply waveform may also bethe result of a simulation of some portion of the power supply network.For the purposes of this description, a representative power supplywaveform comprises an approximation of an actual power supply waveformas occurs in a realistic system. By capturing the power supply waveformat an intermediate point in the power supply network, a division indesign responsibilities and expertise is achieved. A power supplynetwork designer may focus on design and simulation of a portion of thepower supply network while a circuit designer may capture representativepower supply signals at an appropriate location to be used as an inputto their circuits.

[0024] The captured power supply waveform is digitized at (104) to beinput to a simulation program. The digitization may be a direct point bypoint representation. The digitization may also be a representativemodel of the waveform that may include a formulated representation inwhich an equation characterizes the power supply waveform having noise.Capturing and digitizing the power supply waveform does not preclude theaddition of circuits to model another portion of the power supplynetwork not represented in the captured and digitized power supplywaveform. This additional portion of the power supply network may beused between the captured power supply waveform and the circuit underdesign. At (106), elements may be added to the simulation to representadditional power supply network components. For example, a capturedpower supply signal may be captured on a printed circuit board; however,the circuit to be designed resides on an integrated circuit. At (106),the power supply network elements that may be added include, but are notlimited to, connections (parasitics) between the printed circuit boardand chip package, connections (parasitics) between the chip package andchip, and connections (parasitics) between the chip power supply networkand circuit under design. These added elements may improve the modelingof the actual passive parasitics. At (108), the on-chip temperaturesensor under design along with the digitized power supply waveformhaving noise captured from the printed circuit board at (104) and theparasitics from (106) are simulated. At (108), the computationaloverhead of the simulation is reduced due to the input of the powersupply waveform having noise being used instead of a portion of thepower supply network that may contain a large number of elements. Also,the simulation of the on-chip temperature sensor at (108) is moreaccurate because the digitized power supply waveform having noise isused instead of a square wave.

[0025] In FIG. 3b, an exemplary flow process (110) in accordance withanother embodiment of the present invention is shown. At (102), a powersupply waveform having noise, as described previously, is captured. Thecaptured power supply waveform is digitized at (104), as describedpreviously, to be input to a simulation program. At (108), the on-chiptemperature sensor under design along with the digitized power supplywaveform having noise captured from the printed circuit board at (104)are simulated. At (108), the computational overhead of the simulation isreduced due to the input of the power supply waveform having noise beingused instead of a portion of the power supply network that may contain alarge number of elements. Also, the simulation of the on-chiptemperature sensor at (108) is more accurate because the digitized powersupply waveform having noise is used instead of a square wave.

[0026] Those skilled in the art will appreciate that the captured powersupply waveform having noise may be obtained from probing a physicalsystem, such as a printed circuit board, chip package, or chip, undervarious operating conditions. Operating conditions include, but are notlimited to, temperature, voltage, frequency, and manufacturing (process)variations. Those skilled in art will also appreciate that the capturedpower supply waveform having noise may be obtained from probing anintegrated circuit under various operating conditions. Furthermore,those skilled in the art will appreciate that the power supply waveformhaving noise obtained from a physical system may be obtained from alocation adjacent to an intended location of the on-chip temperaturesensor under various operating conditions. Those skilled in the art willfurther appreciate that using the power supply waveform having noise inplace of a portion of the power supply network reduces the computationalload when simulating the circuit.

[0027] Those skilled in the art will appreciate that the captured powersupply signal having noise may be obtained from simulation data of amodeled printed circuit board's parasitics under various operatingconditions. Furthermore, those skilled in art will appreciate that thecaptured power supply waveform having noise may be obtained fromsimulation data of a power supply network's parasitics that may include,but is not limited to, the motherboard power supply network, motherboardto integrated circuit connections, and/or integrated circuit powersupply network under various operating conditions. Operating conditionsinclude, but are not limited to, temperature, voltage, frequency, andmanufacturing (process) variations. Those skilled in the art willfurther appreciate that the simulation of the circuit using the powersupply waveform having noise may be dependent on various operatingconditions. Those skilled in the art will also appreciate that thesimulation tool used to simulate the power supply waveform having noisedoes not have to be the same simulation tool used to simulate thecircuit using the power supply waveform having noise.

[0028] Those skilled in the art will appreciate that capturing the powersupply signal having noise, whether from a physical system orsimulation, may advantageously be obtained adjacent to an intendedlocation of the on-chip temperature sensor.

[0029] Those skilled in the art will appreciate that the noise may becaptured separately from the power supply waveform and combined tocreate the power supply waveform having noise.

[0030] Those skilled in the art will appreciate that multiple powersupply waveforms having noise may be used simultaneously, and themultiple power supply waveforms having noise may be connected todifferent locations on the power supply network. Those skilled in theart will further appreciate that the on-chip temperature sensor andadditional active circuits may be used in the simulation at (108).

[0031] Those skilled in the art will appreciate that the on-chiptemperature sensor may be analog, digital, or a combination of bothtypes of circuits.

[0032] Those skilled in the art will appreciate that the simulation ofthe on-chip temperature sensor may be dependent on at least one selectedfrom the group consisting of temperature, voltage, frequency, andmanufacturing process.

[0033] In FIG. 4, two captured power supply waveforms having noise (202,204), in accordance with various embodiments of the present invention,are shown. Power supply waveform having noise (202, 204) can bedigitized or modeled, and operatively used as the power supply input tothe circuit simulation. Both captured power supply waveforms start attime zero at approximately 1 V. At 10 ns, one or more circuitsinteracting with one or more impedance networks create noise on thepower supply waveforms. For power supply waveform (202), the noiseeffect is reduced compared to power supply waveform (204). Power supplywaveforms having noise (202, 204) are generated using two differentconfigurations of the power supply network. The reduced noise on powersupply waveform (202) may be the result of a more costly configuration.The function of the temperature sensor may be simulated using powersupply waveform (204). If the function of the temperature sensor atleast meets the specification, the power supply network using a lesscostly configuration may be used.

[0034] Those skilled in the art will appreciate that power supplywaveform (202) and power supply waveform (204) may have been capturedunder different operating conditions. Those skilled in the art willfurther appreciate that power supply waveform (202) and power supplywaveform (204) may have been captured at different locations within thepower supply network.

[0035] In FIG. 5, an exemplary circuit (300) in accordance with anotherembodiment of the present invention is shown. A block diagram drawing ofa on-chip temperature sensor (301) is shown. The on-chip temperaturesensor (301) has a temperature representative input sensed by theon-chip temperature sensor (301). The on-chip temperature sensor (301)generates a temperature dependent output (384) such as a binaryrepresentation in response to the temperature representative input.Ideally, a relationship between the temperature representative input andthe value represented by the binary representation is linear. The valuerepresented by the binary representation, however, is affected by powersupply noise.

[0036] Still referring to FIG. 5, a power supply waveform having noisehas been determined from a power supply network and digitized. The powersupply waveform having noise is operatively used either through directdigitization or appropriate modeling such as a formulated representationwhere an equation describes the signal's characteristics. The powersupply waveform having noise is input to an impedance network Z_(M)(390). The impedance network Z_(M) (390) supplies power to the on-chiptemperature sensor (301) through power supply line (392) and ground line(394). Simulating the on-chip temperature sensor (301) with therepresentation of the power supply waveform having noise provides atechnique to estimate the effect of the power supply noise.

[0037] For example, a piece-wise linear representation of the powersupply waveform having noise ((202) (in FIG. 4)) may be used to supplythe impedance network Z_(M) (390). The power supply waveform havingnoise (202) may be acquired from a simulation of a printed circuit boardfrom a dominant power supply noise source. The impedance network Z_(M)(390) represents additional impedances between the printed circuit boardand the on-chip temperature sensor (301) that is located on anintegrated circuit. The power supply waveform having noise may disturbthe temperature sensor (301) such that the value represented by thebinary representation is inaccurate and not within specification. Theaccuracy of the on-chip temperature sensor (301) is defined for thepurposes of this description as the difference between the designedtemperature dependent output (384) and the temperature representativeinput. Because a realistic power supply waveform having noise is used,the on-chip temperature sensor will not be over designed with respect totemperature inaccuracy. Also, the simulation can be completed in areasonable amount of time; therefore, the on-chip temperature sensordesign and/or the chip parasitics may be modified in an iterativefashion to improve the system's performance.

[0038] Those skilled in art will appreciate that a computer system isdescribed for inputting a representation of a power supply waveformhaving noise into a simulation of an on-chip temperature sensor, andestimating accuracy of the on-chip temperature sensor.

[0039] Those skilled in art will appreciate that a computer-readablemedium having recorded thereon instructions executable by a processor isdescribed to input a representation of a power supply waveform havingnoise into a simulation of an on-chip temperature sensor, and estimatingaccuracy of the on-chip temperature sensor.

[0040] Advantages of the present invention may include one or more ofthe following. In some embodiments, because a representative powersupply signal having noise is used, a more accurate circuit simulationmay be performed. Realistic results help alleviate costly over design. Acircuit designed with more accurate power supply waveforms may result inreduced chip area. The space saved due to the reduced chip area may beused for additional performance enhancing circuits, or may be used toreduce the final chip size, hence cost.

[0041] In some embodiments, because a representation of a power supplysignal having noise is used, a circuit simulation that requires lesscomputational load may be performed. Accordingly, more iterations in thedesign process may be afforded.

[0042] In some embodiments, because a representation of a power supplysignal having noise is used, tasks involved with designing a powersupply network and individual circuits may be advantageously divided andperformed by experts in their respective areas of expertise.

[0043] While the invention has been described with respect to a limitednumber of embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. A method for estimating accuracy of an on-chiptemperature sensor, comprising: inputting a representative power supplywaveform having noise into a simulation of the on-chip temperaturesensor; and estimating accuracy of the on-chip temperature sensor fromthe simulation.
 2. The method of claim 1, wherein the representativepower supply waveform is obtained from a physical system.
 3. The methodof claim 2, wherein the physical system comprises a printed circuitboard.
 4. The method of claim 2, wherein the physical system comprises achip package.
 5. The method of claim 2, wherein the physical systemcomprises a chip.
 6. The method of claim 1, wherein the representativepower supply waveform is obtained from a location on a physical systemadjacent to an intended location of the on-chip temperature sensor. 7.The method of claim 1, wherein the representative power supply waveformis obtained from a simulation of a power supply.
 8. The method of claim7, wherein the simulation of the power supply is performed using a firstsimulation tool and the simulation of the on-chip temperature sensor isperformed using a second simulation tool.
 9. The method of claim 1,wherein the representative power supply waveform comprises a noisewaveform combined with a power supply waveform.
 10. The method of claim1, wherein the representative power supply waveform is dependent on atleast one selected from the group consisting of temperature, voltage,frequency, and manufacturing process.
 11. The method of claim 1, whereinthe simulation of the on-chip temperature sensor is dependent on atleast one selected from the group consisting of temperature, voltage,frequency, and manufacturing process.
 12. The method of claim 1, whereinestimating accuracy comprises determining a difference between adesigned temperature dependent binary representation and a temperaturerepresentative input.
 13. A computer system for estimating accuracy ofan on-chip temperature sensor, comprising: a processor; a memory; andsoftware instructions stored in the memory adapted to cause the computersystem to: input a representative power supply waveform having noiseinto a simulation of the on-chip temperature sensor; and estimateaccuracy of the on-chip temperature sensor from the simulation.


14. The computer system of claim 13, wherein the representative powersupply waveform is obtained from a physical system.
 15. The computersystem of claim 14, wherein the physical system comprises a printedcircuit board.
 16. The computer system of claim 14, wherein the physicalsystem comprises a chip package.
 17. The computer system of claim 14,wherein the physical system comprises a chip.
 18. The computer system ofclaim 13, wherein the representative power supply waveform is obtainedfrom a location on a physical system adjacent to an intended location ofthe on-chip temperature sensor.
 19. The computer system of claim 13,wherein the representative power supply waveform is obtained from asimulation of a power supply.
 20. The computer system of claim 19,wherein the simulation of the power supply is performed using a firstsimulation tool and the simulation of the on-chip temperature sensor isperformed using a second simulation tool.
 21. The computer system ofclaim 13, wherein the representative power supply waveform comprises anoise waveform combined with a power supply waveform.
 22. The computersystem of claim 13, wherein the representative power supply waveform isdependent on at least one selected from the group consisting oftemperature, voltage, frequency, and manufacturing process.
 23. Thecomputer system of claim 13, wherein the simulation of the on-chiptemperature sensor is dependent on at least one selected from the groupconsisting of temperature, voltage, frequency, and manufacturingprocess.
 24. The computer system of claim 13, wherein estimatingaccuracy comprises determining a difference between a designedtemperature dependent binary representation and a temperaturerepresentative input.
 25. A computer-readable medium having recordedthereon instructions executable by a processor, the instructions adaptedto: input a representative power supply waveform having noise into asimulation of an on-chip temperature sensor; and estimate accuracy ofthe on-chip temperature sensor from the simulation.
 26. Thecomputer-readable medium of claim 25, wherein the representative powersupply waveform is obtained from a physical system.
 27. Thecomputer-readable medium of claim 26, wherein the physical systemcomprises a printed circuit board.
 28. The computer-readable medium ofclaim 26, wherein the physical system comprises a chip package.
 29. Thecomputer-readable medium of claim 26, wherein the physical systemcomprises a chip.
 30. The computer-readable medium of claim 25, whereinthe representative power supply waveform is obtained from a location ona physical system adjacent to an intended location of the on-chiptemperature sensor.
 31. The computer-readable medium of claim 25,wherein the representative power supply waveform is obtained from asimulation of a power supply.
 32. The computer-readable medium of claim31, wherein the simulation of the power supply is performed using afirst simulation tool and the simulation of the on-chip temperaturesensor is performed using a second simulation tool.
 33. Thecomputer-readable medium of claim 25, wherein the representative powersupply waveform comprises a noise waveform combined with a power supplywaveform.
 34. The computer-readable medium of claim 25, wherein therepresentative power supply waveform is dependent on at least oneselected from the group consisting of temperature, voltage, frequency,and manufacturing process.
 35. The computer-readable medium of claim 25,wherein the simulation of the on-chip temperature sensor is dependent onat least one selected from the group consisting of temperature, voltage,frequency, and manufacturing process.
 36. The computer-readable mediumof claim 25, wherein estimating accuracy comprises determining adifference between a designed temperature dependent binaryrepresentation and a temperature representative input.